Heat dissipating assembly

ABSTRACT

A heat dissipating assembly includes a substrate configured to support at least one heat producing component and a thermally conductive cooling fin extending from the substrate, wherein heat is conducted away from the heat producing component.

BACKGROUND OF THE INVENTION

Heat producing devices, such as printed circuit boards, often containheat producing components, such as processors or voltage regulators,which generate heat in sufficient amounts that may impact theperformance of the device, unless the heat is removed. A thermal planemay be provided in combination with the heat producing devices to forman assembly to aid in the removal of heat, typically by providingadditional conductive pathways to disperse the heat.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a heat dissipating assembly includes a substrateconfigured to support at least one heat producing component, a thermallyconductive cooling fin extending from the substrate, and a thermallyconductive heat pipe conductively coupled to the heat producingcomponent, extending within at least a portion of the cooling fin, anddefining a fluid reservoir containing a phase change fluid. The phasechange fluid changes between a liquid and a gas in response to heatconducted from the heat producing component to the heat pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic cross-sectional view of a heat producing device inthe form of a printed circuit board assembly in conductive contact withthe heat dissipating assembly according to one embodiment of theinvention.

FIG. 2 is an exploded cross-sectional view of the heat dissipatingassembly according to one embodiment of the invention.

FIG. 3 is a top-down view of a heat pipe, taken along line 3-3 of FIG.2, according to one embodiment of the invention.

FIG. 4 is a cross-sectional view of the heat pipe illustrating theoperation of the heat transfer.

FIG. 5 is a perspective view of the heat dissipating assembly and piezocooler device, according to a second embodiment of the invention.

FIG. 6 is a top-down view of the heat pipe, taken along line VI-VI ofFIG. 5, according to a second embodiment of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The embodiments of the present invention are related to a heatdissipating assembly configured to provide cooling to a heat producingcomponent. In the embodiment of FIG. 1, a printed circuit board (PCB)assembly 10 is shown comprising a PCB 12 having at least one heatproducing component 14, such as a microprocessor, or silicon carbinemetal-oxide semiconductor field effect transistor (MOSFET).

The PCB assembly 10 is shown proximate to a heat dissipating assembly 16having a thermally conductive substrate 18, at least one thermallyconductive cooling fin 20, and a thermally conductive heat pipe 22. Eachof the substrate 18, cooling fin 20, and heat pipe 22 may be machined ormanufactured from a same or dissimilar material having a high thermalconductivity. Non-limiting examples of materials having a high thermalconductivity may include aluminum, copper, or various alloys. Forpurposes of the invention, the type of material is not limiting. Allthings being equal, the higher the thermal conductivity the better.Lesser thermal conductive will merely reduce the heat transferperformance.

At least a portion of the substrate 18 may be in thermally conductiverelationship with the heat producing component 14 such that heatgenerated by the heat producing component 14 may be conducted to thesubstrate 18. For example, as shown, the substrate 18 may support and/orabut the heat producing component 14. Additionally, embodiments of theinvention may include, for example, a layer of thermally conductivematerial, such as a thermal epoxy, between the substrate 18 and the heatproducing component 14, to provide for increased thermal conductivitybetween the heat producing component 14 and the heat dissipatingassembly 16.

The cooling fins 20 are thermally coupled with, and extend away from,the substrate 18, opposite the PCB assembly 10. The cooling fin 20 maybe configured to provide for removing heat, for example, by convection,when exposed to a fluid, such as air, gas coolant, or liquid coolant.Example configurations for removing heat by convection may includedesigning the cooling fin 20 having a geometric cross-sectional shape,such as a square, circle, triangle, ellipse, etc., to increase surfacearea for convection to take place. Additional embodiments of theinvention may further include, for example, a patterned outer surface.As shown, embodiments of the invention may include a plurality ofcooling fins 20, which may be arranged in an arrayed-type pattern, andpositioned proximate to the heat producing component 14.

Each cooling fin 20 may further include a conductively coupled heat pipe22, configured in an elongated shape, such as a cylinder, located withinthe fin 20, and extending along at least a portion of the fin 20. Inthis sense, the elongated heat pipe 22 includes a first end 24 proximateto, and conductively coupled, including direct and indirect abutment,to, the substrate 18 and an opposing second end 26 being distal from thesubstrate 18, along the extended portion of the fin 20. The heat pipe 22may further include an inner surface 28 defining a fluid reservoir 30containing a phase change fluid 32, which may, for example, changephases from a liquid to a gas.

The phase change fluid 32 may be selected or configured to provide for aparticular heat of vaporization, or enthalpy of vaporization, which isthe combined internal energy and enthalpy change required to transform agiven quality of a fluid from a liquid into a gas, at a given pressure.In this sense, the heat of vaporization of the phase change fluid 32defines the amount of heat absorbed by the fluid 32 to change the phaseof the fluid 32 from a liquid to a gas, and conversely, how much heat isreleased from the fluid 32 when the gas condenses back to a liquid.Furthermore, embodiments of the invention may include a sealed heat pipe22 configuration such that the pressure within the fluid reservoir 30may be modified to provide a selected heat of vaporization. Theparticular phase change fluid 32 may be selected based on the expectedtemperatures to be encountered during the operation of the heatdissipating assembly to ensure the phase change will occur. Non-limitingexamples of phase change fluids 32 that may be utilized include water,ammonia, methanol, acetone, Freon, or any combination thereof Phasechange fluids 32 may further be selected based on their compatibilitiesor incompatibilities with the heat pipe 22 materials or construction.

While the illustrated example shows the phase change fluid 32 poolednear the second end 28 of the heat pipe 22, embodiments of the inventionmay include a heat pipe 22 configuration with a relatively smallcross-sectional area or diameter, such that circulation of the fluid 32occurs without the assistance of, and sometimes in opposition to,external forces such as gravity. This type of circulation is known ascapillary action, and may provide for a heat pipe 22 configuration wheregravitational effects on the phase change fluid 32 is negligible. Statedanother way, embodiments of the invention may include a heat pipe 22configuration wherein the phase change fluid 32 is dispersed over theentire fluid reservoir 30, as opposed to pooled at one end 24, 28 of thereservoir 30. Another effect of the above-described capillary actionembodiment may include a heat pipe 22 configuration where, due to thedispersing of the phase change fluid 32, may be configured in anyorientation.

FIG. 2 illustrates an exploded cross-sectional view of the heatdissipating assembly 16 of FIG. 1. As shown, the heat pipe 22 may beindependently constructed and/or configured, and assembled into thecooling fin 20, for example, through an opening 33 of the substrate 18,cooling fin 20, and/or heat dissipating assembly 16, at a later time. Inthis example, at least a portion of the heat pipe 22 may include, forexample, a mechanical fastener configuration, illustrated as the heatpipe 22 including a screw 34 having a threaded exterior surface 36. Thecooling fin 20 may correspondingly be configured to receive themechanical fastener, such as a threaded inner surface 38, as shown. Inthis configuration, the heat pipe screw 34 may be fixedly or removablyreceived within the cooling fin 20, through the opening 33, duringassembly.

Embodiments of the heat dissipating assembly 16 may further include asecond substrate portion 40 which may fixedly or removably provide orrestrict access to the heat pipe 22 and/or the opening 33. The secondsubstrate portion 40 may comprise the same as, or a different materialthan, the substrate 18. For example, in a configuration where the secondsubstrate portion 40 may directly abut the heat producing component 14,it may be desirable to configure the second substrate portion 40 as adifferent material that better matches the coefficient of thermalexpansion of the heat producing component 14 to ensure a reliablethermal contact between the component 14 and substrate 18 occurs.

FIG. 3 illustrates a cross section of the inner surface 28 of the heatpipe 22, according to one embodiment of the invention. In this example,the inner surface 28 may comprise a patterned sidewall 42, shown assemi-circular ridges radially arranged about the surface 28 that may besized to provide for the capillary action of the phase change fluid 32.As explained above, the interaction of the phase change fluid 32 withthe patterned sidewall 42 creates a capillary action which draws andstores the fluid 32 along the elongated shape of the heat pipe 22,ensuring a reliable thermal conductivity between the fluid 32 and theheat pipe 22.

Embodiments of the heat pipe 22 may include, for example, machining thepatterned sidewall 42 into the inner surface 28, or forming the sidewall42 during casing of the pipe 22. Additional manufacturing or assemblyembodiments of the heat pipe 22 may be included. While the heat pipe 22is illustrated having a circular cross section, embodiments of theinvention may include alternative cross-sectional pipe 22 shapes, suchas a square, triangle, ellipse, etc. Furthermore, additional patternedsidewalls 42 may be included in embodiments of the invention. Thepattern of the sidewalls 42 may be configured based on the phase changefluid 32 to provide for optimized capillary action, as explained above.

Alternatively, embodiments of the invention may include, for example, ascrew casing, wherein the heat pipe 22 may be fixed, such as byadhesive, into the screw casing, which may then be received by thethreaded inner surface 38 of the cooling fin 20. In another alternativeembodiment of the invention, the heat pipe 22 may be integrated ormachined directly into the cooling fin 20. In yet another alternativeembodiment of the invention, at least one of the threaded exteriorsurface 36 of the heat pipe 22 or threaded inner surface 38 of thecooling fin 20 may include a thermally conductive later, such as tape, acoating, or an epoxy, to provide for increased thermal conductivity or amore reliable thermal contact.

FIGS. 2, 3, and 4 illustrate the heat transfer cycle of the heat pipe 22and phase change fluid 32. The substrate 18, cooling fin 20, and heatpipe 22 are each configured in a thermally conductive relationship witheach other such that a heat conduction path may exist,tri-directionally, between the components 18, 20, 22. Thus, in oneexemplary scenario, heat generated by the heat producing component 14 isconductively transferred to the substrate 18, which may be furtherconductively transferred to the heat pipe 22 (In FIG. 4, illustrated asarrows 44), for example, via the first end 24 of the pipe 22, and/or viathe substrate 18 to the cooling fin 22, and from the cooling fin 20 tothe pipe 22. The heat conducted to the heat pipe 22 may then beconductively transferred to, or absorbed into, the phase change fluid32, which, in response to the heat conducted from the substrate 18and/or cooling fin 22, changes phases from a liquid to a gas(illustrated as dotted line 46), absorbing at least a portion of theheat.

In FIG. 4, the phase change fluid gas 46, may traverse along at least aportion of the heat pipe 22 and condense (i.e. change phase back to aliquid) along the inner sidewalls 42 of the heat pipe 22, releasing thestored portion of the heat (illustrated as arrows 48) into a wall 42 ofthe heat pipe 22, or to the cooling fin 20. The heat may then, forexample, be released to the local ambient air surrounding the coolingfin 20. In this example, a portion of the elongated heat pipe 22 spacedfrom the substrate 18 and heat producing component 14, and/or theextension of the cooling fin 20 corresponding to, and in a thermalrelationship with, the pipe 22, may be cooler, or at a lowertemperature, than another portion of the pipe 22 and fin 20 proximate tothe substrate 18 and component 14. The phase change fluid liquid, inturn, disperses back toward the heat producing component 14, along thepatterned sidewalls 42 of the inner surface 28, by capillary action(illustrated by arrow 54), ready to absorb (?) heat.

In this sense, the substrate 18, heat pipe 22, and cooling fin 20 areconfigured such that heat generated by the heat producing component 14is absorbed by at least the heat pipe 22, and consequently, the phasechange fluid 32 when vaporizing, and is carried away, or removed fromthe heat producing component 14 and/or substrate 18 by the phase changefluid 32 gas, to another portion of the heat pipe 22, spaced away fromthe heat producing component 14. At the another, cooler, portion of theheat pipe 22, the phase change fluid 32 gas condenses along thepatterned sidewall 42 along the inner surface 28 of the pipe 22,releasing the heat back into the pipe 22 and consequently, the coolingfin 20 relative to the another portion of the pipe 22. The cooling fin20 may then further dissipate the heat to the local environment, viaconvection, as explained above.

FIG. 5 illustrates an alternative heat dissipating assembly 116according to a second embodiment of the invention. The second embodimentis similar to the first embodiment; therefore, like parts will beidentified with like numerals increased by 100, with it being understoodthat the description of the like parts of the first embodiment appliesto the second embodiment, unless otherwise noted. A difference betweenthe first embodiment and the second embodiment is that heat pipe 122 ofthe second embodiment may be configured having a fixed or removablefirst end 124, and may be received directly into the opening 133 of thesubstrate 118 such that the first end 124 may abut a heat producingcomponent 14 (not shown) directly.

Another difference between the first embodiment and the secondembodiment is that heat dissipating assembly 116 of the secondembodiment may further include a component configured to generate afluid movement across the cooling fins 20 to provide increasedconvection cooling of the fins 20. In the illustrated example, a piezocooler 150 may produce a jet of air (shown as arrows 152) across thecooling fins 20.

FIG. 6 illustrates a cross section of the inner surface 128 of the heatpipe 122, according to the second embodiment of the invention. In thisexample, the inner surface 128 may comprise an alternatively patternedsidewall 142, shown having inverse semi-circular ridges, compared to thepatterned sidewall 42 of the first embodiment, radially arranged aboutthe surface 128.

Many other possible embodiments and configurations in addition to thatshown in the above figures are contemplated by the present disclosure.For example, while the above-described examples of heat producingcomponents 14 may primarily described as types of electrical components(e.g. resistors, inductors, capacitors, power regulators, pulse lasercontrol boards, etc.), embodiments of the invention may be applicable toalternative heat dissipating or cooling configurations, for example, indissipating heat from coolant or oil in a generator, or in dissipatingheat from a line replaceable unit, for example, in an aircraft.Furthermore, while only a single heat producing component 14 isillustrated, embodiments of the invention may include pluralities ofheat pipes 22 and cooling fins 20 to account for additional heatproducing components 14 associated with a single heat dissipationassembly 16. The pluralities of heat pipes 22 and cooling fins 20 may begrouped proximate to the respective heat producing components 14, ordistributed across at least a portion of the substrate 18.

Furthermore, the configuration of the heat dissipating assembly 16,including, for example, cooling fin 20 size, length, and height, or heatpipe 22 length and phase change fluid 32 composition, may be selectedbased on the heat dissipation needs of a particular application, or toensure a desired cooling temperature. For instance, a high heat flux, ortransient duration heat producing component 14 may have different heatdissipating needs than a heat producing component 14 that generates asteady state heat flux, and thus may need additional heat dissipatingmeans. Likewise, a heat producing component 14 of a line-replaceableunit on an aircraft may have size or height restrictions for coolingfins 20. In yet another example, a heat dissipating assembly 16 exposedto liquid coolant may be configured with a smaller, or shorter heat pipe22 and/or cooling fins 20, due to improved heat dissipation from thefins 20 to the liquid coolant.

In yet another embodiment of the heat dissipating assembly 16, more thanone heat pipe 22 may be coupled with a single cooling fin 20, forexample, in a stacked configuration along the extending direction of thefin 20, to provide for increased heat dissipation. In even yet anotherembodiment of the heat dissipating assembly 16, the cooling fins 20 mayfurther comprise a coating, such as a lusterless black coating includinga mixture of carbon black particles, configured to remove and/ordissipate additional heat from at least one of the heat pipe 22 orsubstrate 18 by radiation. Additionally, the design and placement of thevarious components may be rearranged such that a number of differentconfigurations could be realized.

The embodiments disclosed herein provide a heat dissipating assemblyhaving a heat pipe. One advantage that may be realized in the aboveembodiments is that the above described embodiments have superior weightand size advantages over the conventional type heat dissipatingassemblies having air cooling fins, or assemblies including, forinstance, fans or liquid cooling components, to provide for coolingcapabilities. Furthermore, the heat pipe provides for reduced weight,compared with a solid pin fin assembly, and provides for approximatelyeight times greater thermal conductivity. The thermal management systemof coupling radiation, convection, and conduction provides for a heatdissipation assembly that competes with actively-cooled heat managementsystems (e.g. with fans, pumped coolant, etc.)

With the proposed heat dissipation assembly, a high heat dissipation canbe achieved during transient or steady state heat conditions withoutadditional heat dissipation elements, thus increasing the reliability ofsuch heat dissipation assemblies by reducing the need for additionalcomponentry. In addition to increased reliability, reducing componentsdirectly relates to reducing weight and volume of the assembly, and isespecially beneficial in space and weight-limiting applications, such asairborne platforms. Moreover, higher heat producing componentreliability can be achieved even when components do not have high heatconditions.

When designing heat dissipation assemblies, important factors to addressare power, size, weight, and reliability. The above described heatdissipation assemblies have a decreased number of parts compared to aheat dissipating assembly having active air or liquid cooling, makingthe complete system inherently more reliable. This results in a lowerelectrical power, lower weight, smaller sized, increased performance,and increased reliability system. The lower number of parts and reducedmaintenance will lead to a lower product costs and lower operatingcosts. Reduced weight and size correlate to competitive advantages.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A heat dissipating assembly, comprising: asubstrate configured to support at least one heat producing component; athermally conductive cooling fin extending from the substrate; and athermally conductive heat pipe conductively coupled to the heatproducing component, extending within at least a portion of the coolingfin, and defining a fluid reservoir containing a phase change fluid;wherein the phase change fluid changes between a liquid and a gas inresponse to heat conducted from the heat producing component to the heatpipe.
 2. The heat dissipating assembly of claim 1 further comprising aplurality of cooling fins and a plurality of heat pipes, wherein eachheat pipe extends within at least a portion of a respective cooling fin.3. The heat dissipating assembly of claim 2 wherein the plurality ofcooling fins are arranged in an array.
 4. The heat dissipating assemblyof claim 1 wherein at least one of the heat pipe or cooling fin islocated proximate to the at least one heat producing component.
 5. Theheat dissipating assembly of claim 1 wherein the heat pipe furthercomprises mechanical fastener configured to couple with the cooling fin.6. The heat dissipating assembly of claim 1 wherein the heat pipefurther comprises a screw having a threaded exterior surface, whereinthe screw is threaded into the cooling fin and the heat pipe is locatedwithin the screw.
 7. The heat dissipating assembly of claim 6 whereinthe screw further comprises an elongated shape having a first endproximate to the substrate and an opposing second end being distal fromthe substrate.
 8. The heat dissipating assembly of claim 7 furthercomprising a thermally conductive material between the threaded exteriorsurface of the screw and the cooling fin.
 9. The heat dissipatingassembly of claim 1 wherein the heat pipe further comprises an elongatedshape having a first end proximate to the substrate and an opposingsecond end being distal from the substrate.
 10. The heat dissipatingassembly of claim 9 wherein the heat pipe further comprises an innersurface defining the fluid reservoir, wherein the inner surface isconfigured to provide for capillary action along the elongated shape.11. The heat dissipating assembly of claim 9 wherein the elongated shapeof the heat pipe further comprises a cross section configured to negategravitational effects on the phase change fluid so that the heat pipeoperates in any orientation.
 12. The heat dissipating assembly of claim1 wherein the cooling fin is configured to remove heat from at least oneof the heat pipe or substrate by convection.
 13. The heat dissipatingassembly of claim 12 wherein the cooling fin is exposed to a fluid. 14.The heat dissipating assembly of claim 1 wherein the cooling fin furthercomprises a coating configured to remove heat from at least one of theheat pipe or substrate by radiation.
 15. The heat dissipating assemblyof claim 1 wherein the substrate comprises an alloy configured to matchthe coefficient of thermal expansion of the at least one heat producingcomponent.